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what should the RPM's be?

  • Thread starter Thread starter Morgan
  • Start date Start date
M

Morgan

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At a specific speed and gear, say 100km/h or 60mph and 5th gear (or any other combo), what sort of engine RPM's I should be getting for a 1979 GS850G? My bike is finally on the road, and I noticed that the RPM's were about 2700 in fifth at an indicated 80km/h, which to me seems high, but I have nothing to compare it to.

Thanks,
Morgan
 
Most bikes I've been around, 750 & up, you can figure 1,000 rpm = 15 mph in high gear. 2000 = 30mph, 3,000 = 45mph, 4,000 = 60mph etc. Different bikes are different, but this should be in the ballpark
 
I have a '79 1000. At 4000 rpm I'm doing 67 mph. At about 3600 rpm I'm doing 60.
 
Morgan,

I'll check either tonight, or no later than tomorrow. But only 2700 rpm's at 50 mph does not sound right, based on my GS850. Your rpm's seem quite low, but I could be mistaken. Will let you know.
 
I have some info on the '79 850 from road tests in Cycle and Cycle Guide magazines. According to Cycle at 60 mph the engine is turning 4460 rpm in top (5th) gear. Cycle guide gives the following mph x rpm figures which work out pretty close to those numbers.

1st gear - 5.3 mph per 1000 rpm
2nd gear - 7.4 mph per 1000 rpm
3rd gear - 9.5 mph per 1000 rpm
4th gear - 11.7 mph per 1000 rpm
5th gear - 13.7 mph per 1000 rpm

At 2700 rpm in top gear you should be doing about 37 mph. Or at 50 mph you should be running 3650 rpm.

I have found these numbers to be spot on with my 80 850. I had a crankshaft-up rebuild done on it a couple of years ago and was off of it for 3 months. When I go it back it felt like it was geared lower than before even though I knew that couldn't be with a shaft drive bike. I called the local Sheriff's office and asked where the smart trailers would be. Those are the little radar signs that read your speed as you approach them; you sometimes see them in construction areas or at the airport terminal.

I made numerous passes on several different occasions and found out that my speedometer is spot on and in fact may be a little under (60 on my speedometer, 61 on the radar trailer). And sure enough my tach was touching the 4500 mark.

Most speedos are actually a little optimistic; it is common for a speedo to be showing 60 when the true speed is 55. You should first get yours calibrated and then you should be able to apply the ratios above. Either you have a very optimistic speedometer, or your tach is way lazy.

If there was one thing I could change about the 850, it would be to give it a 6th gear for highway cruising.

P.S.

1980 GS1000E 15.8 mph per 1000 rpm in 5th
1980 GS1000g 15.4 mph per 1000 rpm in 5th
 
Message deleted - Redundant of previous one.
 
wow, 75 MPH in 6th gear in my 78 GS550 was ~7000 RPM. 8O

my new 550's speedometer acts kinda slow...so i use the function: at 5000 RPM - (Gear Number) x 10. So, 4th gear, 5000 RPM is about 40 MPH...estimate. works for me. 8)

~Adam
 
Took the 850 out for a ride this morning and checked.

At 50 mph (80 kmh), tachometer says between 3600 and 3700 rpms.
 
You guys are lucky.

@100km/h
4th = 8000
5th = 7000
6th = 6000

Steve
 
Thanks for the info guys!

I got the bike out again, and now the revs seem more in line with what they should be. My guess is that the cable or the gears in the speedo might have been a little bit stiff with age and no use and got loosened up a bit when I went riding. I don't think it was the tach, since had gotten a regular workout while working on the engine. Okay, I admit it, it got a workout even when the engine didn't need work; I would just fire it up to listen to it every once and a while. :lol: I love the sound that motor makes.

I know what you guys mean by looking for sixth, my CM450 is a six speed, and I had to continually remind myself that the GS was not while I was on it. The GS is also a hellovalot faster, something I kinda deliberately forgot to remind myself. :twisted:

-Morgan
 
Holy crap!
An 8 year old thread risen!

But yeah, my 650 is at like 7000rpm's at around 65mph-70.
 
I thought the same thing... 2003?

Who spent the time to dig this up lol.
 
Morgan said:
I noticed that the RPM's were about 2700 in fifth at an indicated 80km/h, which to me seems high, but I have nothing to compare it to.

Thanks,
Morgan
Click to expand...

My 850 and 1000 G models are running about 4,500 at 100km/h.
Sounds about right to me! ;)

Daniel
 
ehh it happens sometimes I guess.

I've sat for 30 minutes before, typing up this big elaborate response, then realize the thread is like 5 years old.....i'm like ****!!!
 
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